Managing Aspen Habitat for Birds
in the Sierra Nevada
Aspen are often out-competed by conifers in the Sierra Nevada, due to extensive livestock grazing and
the absence of regular fire. As a result, the health of aspen has deteriorated and estimates suggest its
extent in western North America has been reduced by as much as 96%. Aspen habitat, especially when
associated with riparian vegetation, is the single most species-rich avian habitat in the Sierra Nevada.
Several bird species of management interest are associated with aspen including Northern Goshawk,
Red-breasted Sapsucker, Warbling Vireo, and Mountain Bluebird. With its disproportionate importance
to birds and other wildlife, limited extent on the landscape, and significant loss and degradation, aspen
restoration should be among the highest priorities of land managers in the Sierra Nevada.
Key Aspen Bird Species
Northern Goshawk
Red-breasted Sapsucker
Warbling Vireo
Western Wood-Pewee
Dusky Flycatcher
Tree Swallow
Mountain Bluebird
Swainson’s Thrush
Chipping Sparrow
Sandy Scoggin
EricPreston.com
With the extensive loss and degradation of aspen throughout the
Sierra, large-scale restoration efforts are called for to avoid further
losses and increase the ecological value of this vital habitat. The
following are a list of the most important considerations for managing
aspen for breeding birds:
1. Promote aspen regeneration and expansion. This is the
single most important management consideration to avoid further
losses and degradation of this important habitat.
2. Manage for multiple age and cover classes. Smallest size
classes of aspen are important predictors of avian richness.
3. Restore riparian aspen communities. When healthy, this is
the single most species-rich habitat in the Sierra, supporting
numerous birds species of management concern.
4. Manage for dense and diverse understory. Understory aspen and riparian shrubs are important for numerous avian species.
5. Limit grazing and over-browsing. Grazing and over-browsing
can significantly reduce aspen regeneration, understory foliage
volume, and the structural diversity important for numerous bird
species. Grazing may also increase cowbird abundance which can
negatively impact breeding birds.
Peter LaTourrette
Peter LaTourrette
Mountain Bluebird
Strategies for Enhancing Aspen Bird Habitat
Key Habitat Features
Structural diversity
Dense herbaceous layer
Decay in Live stems
Cavities
Multiple size classes
Riparian shrub understory
Tree Swallow exiting aspen nest cavity
Adaptive Management
Response to Treatment
EricPreston.com
A vital part of effective aspen management is developing a monitoring and adaptive
feedback framework. As aspen restoration treatments are a new practice in the Sierra
Nevada, monitoring the treatment effects on the ecosystem and feeding information
back into future management actions will result in the greatest benefit to wildlife and
achieving other restoration objectives. Bird monitoring is an ideal tool for providing
cost-effective feedback on a whole community of organisms.
In the Eagle Lake Ranger District (ELRD) of the Lassen National Forest (LNF), within Red-breasted Sapsucker
five years treated stands had higher species richness and abundance of most key aspen species, including
woodpeckers, Mountain Bluebird, and Chipping Sparrow. Treated sites were flush with new aspen growth
and a lush understory vegetation community. We expect restored sites to support even greater avian
diversity and abundance as more structural complexity and foliage volume develops at treated sites.
Cavity Nesting Birds
0.8
Mean Detections per Point
Numerous studies have shown aspen is an important
habitat for cavity nesting birds. In the ELRD woodpeckers were 2 to 3 times more abundant at restored aspen
sites than either untreated aspen or non-aspen conifer
sites (see figure). Woodpeckers play a vital role by
creating cavities for use by a vast array of birds and
other wildlife species. Key management actions to
benefit cavity nesting birds:
♦ Significantly reduce conifer cover
♦ Retain dead and dying aspen stems
♦ Retain large conifer snags & some large logs
Treated A spen
0.7
Untreated A spen
0.6
No n-A spen
0.5
0.4
0.3
0.2
0.1
0
Hairy
Wo o dpecker
Red-breasted
Sapsucker
A ll
Wo o dpeckers
8
6
4
2
Avian Species Richness
10
Structural Diversity
The great structural diversity associated with healthy
aspen stands is likely a primary reasons this habitat
supports such a diverse assemblage of avian species. In
the ELRD, the best predictor of avian richness was
understory aspen stems. This feature has been lost in
many stands due to overgrazing and browsing, and
conifer encroachment.
Ensuring that this habitat
component is represented on the landscape in
perpetuity is critical to providing high quality aspen bird
habitat. Structural diversity can be achieved by:
♦ Aspen release through conifer removal
♦ Limiting grazing and over-browsing of stands
♦ Removing excessive conifer duff and slash
0
50
100
150
200
# of Understory Aspen Stems
Aspen Resources
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Aspen Delineation Project
www.aspensite.org/
Lassen National Forest Aspen Restoration Team
trickman@fs.fed.us
Riparian Bird Conservation Plan
www.prbo.org/calpif/htmldocs/riparian.html
US Forest Service RMRS Aspen Restoration Site
www.fs.fed.us/rm/aspen/
PRBO Conservation Science Sierra Nevada Program
rburnett@prbo.org
US Forest Service PSW Sierra Nevada Research Center
www.fs.fed.us/psw/programs/snrc/
Funding Provided by: The National Fire Plan and USDA Forest Service: Region 5, Lassen National Forest, & HFQLG Monitoring Funds.